Olive Knuckle hinges, some times also referred to as cocoon hinges have been manufactured without much change in design for well over 200 years. An example of a prior art hinge may be seen in U.S. Pat. No. 2,566,504 to Soss. Additional examples may be viewed in the Stanley catalog #15 circa 1910 page 31, the Stanley 1997 catalog page 81, the Yale catalog #26 1926 page 480, the Rixson catalog of January 1930 page 6, the P. E. Guerin period hardware catalog of 1914 page 316, and the P. E. Guerin 1997 catalog.
These hinges involve two halves each with a leaf and a knuckle, a pivot shaft partially inserted into a bore between each knuckle and a thrust bearing between the two knuckles, trapped in place by the pivot shaft running through it. Usually the pivot shaft is pressed into one knuckle. The portion of the half that is designed to be attached to a door or frame is referred to as the leaf, and the thickened portion of each half which mates with a pivot shaft is referred to as the knuckle.
The only provision for a bearing in the prior art designs is the central ring thrust bearing. If all the weight of the connecting door were directly in line and above the pivot shaft of the hinge, this would be a good design. The weight however, is not directly above nor inline with the pivot shaft. The weight of the door extends out several feet from the hinge. This puts a great cantilever force on the pivot shaft, the surrounding bore of the hinge knuckles, as well as an uneven force on the thrust bearing. This uneven cantilever force causes the bores in each hinge to wear quickly and unevenly, causing a loose and imperfect fit. The thrust bearing also wears quickly in an uneven pattern preventing a smooth and easy motion of the hinge.
Although beautiful in appearance, because of their wear problems, prior art knuckle hinges are recommended by their manufacturers only for use on low frequency, light weight doors.
An additional problem with the prior art is that the thrust bearing is a central visual point of the hinge, and due to its necessity to bear weight it cannot be made to be decorative nor of non-load-bearing materials.
Accordingly there exists a need in the art for an improved knuckle hinge which provides for reduced wearing, increased loading capabilities and which allows for the central thrust bearing ring to be eliminated or made a decorative element.